Drive control apparatus for hybrid vehicle

ABSTRACT

A drive control apparatus for a hybrid vehicle which has an engine selectively set in one of a normal fuel-consumption operation mode and a low fuel-consumption operation mode for obtaining a lower fuel consumption; a generator selectively used for one of being driven by the engine and assisting driving of the engine; a motor for generating a driving force of the vehicle by electric power supplied by the generator or a battery device; and a clutch between the generator and wheels of the vehicle. The drive control apparatus has a control part for performing a low fuel-consumption driving assistance mode when the engine is set in the low fuel-consumption operation mode. In the low fuel-consumption driving assistance mode, the clutch is connected, and driving of the vehicle is assisted using one of the generator and the motor, which is selected in accordance with an operation state of the vehicle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a drive control apparatus for a hybridvehicle which can run in a low fuel-consumption mode, in particular, ahybrid vehicle having a generator driven by an engine, and an (electric)motor driven by the generator or a battery device.

Priority is claimed on Japanese Patent Application No. 2006-126712,filed Apr. 28, 2006, the content of which is incorporated herein byreference.

2. Description of the Related Art

In a known example of a hybrid vehicle, a front motor is coupled to acrank shaft of an engine which can operate in a cylinder stop (or idle)mode, the front motor is connected to front wheels via a front clutch,and a rear motor is connected to rear wheels via a rear clutch. In anengine running mode, the hybrid vehicle runs with the front clutchconnected so as to drive the engine, and in a first EV running mode ofthe hybrid vehicle, the engine is stopped and the front clutch isdisconnected while the rear clutch is connected, so as to stop the frontmotor and run by only using the rear motor. In a second EV running modeof the hybrid vehicle, the engine is operated in a cylinder stop mode,the front clutch is disconnected, and the rear clutch is connected, soas to drive the front motor and run by only using the rear motor.

In accordance with the above hybrid vehicle, fuel consumption can bereduced (i.e., improved) by enlarging a range or area in which thevehicle can run using only the motor while the engine is stopped (seeJapanese Unexamined Patent Application, First Publication No.2004-208477).

In the above conventional structure, fuel consumption can be improved bycombining the enlargement of the running range using the motor with thecylinder stop operation. However, when the vehicle runs using only themotor, the motor may be used in an inefficient range.

SUMMARY OF THE INVENTION

In light of the above circumstances, an object of the present inventionis to provide a drive control apparatus for a hybrid vehicle, forproviding most efficient driving in consideration of the operation stateof the generator or the motor.

Therefore, the present invention provides a drive control apparatus fora hybrid vehicle, wherein:

the hybrid vehicle comprises:

an engine (e.g., an engine E in an embodiment described later) which isselectively set in one of a normal fuel-consumption operation mode(e.g., a V6 operation mode in the embodiment) and a low fuel-consumptionoperation mode (e.g., a cylinder-stop operation mode in the embodiment)for obtaining a lower fuel consumption in comparison with the normalfuel-consumption operation mode;

a generator (e.g., a second motor M2 in the embodiment) selectively usedfor one of being driven by the engine and assisting driving of theengine;

a motor (e.g., a first motor M1 in the embodiment) for generating adriving force of the vehicle by electric power supplied by the generatoror a battery device (e.g., a battery LB in the embodiment); and

a clutch (e.g., a clutch C in the embodiment) provided between thegenerator and wheels (e.g., wheels W in the embodiment) of the vehicle,and

the drive control apparatus comprises:

a control part for performing a low fuel-consumption driving assistancemode (refer to steps S065, S066, and S068 in the embodiment) when theengine is set in the low fuel-consumption operation mode, wherein in thelow fuel-consumption driving assistance mode:

the clutch is connected; and

driving of the vehicle is assisted using one of the generator and themotor, which is selected in accordance with an operation state of thevehicle.

In accordance with the above structure, a required driving force to beassisted (or a required acceleration) can be provided by assisting thedriving force of the engine while the low fuel-consumption operationmode is maintained. Therefore, the fuel consumption can be furtherimproved, thereby improving salability.

Preferably, when one of the generator and the motor is selected, onehaving a higher efficiency is selected. Accordingly, the driving forceassistance of the vehicle can be performed with a minimum loss, therebyimproving the fuel consumption.

In a preferable example, the drive control apparatus includes:

a vehicle speed measuring device (e.g., a vehicle speed sensor in theembodiment) for measuring a vehicle speed (e.g., a vehicle speed VP inthe embodiment) of the vehicle, wherein:

when the vehicle speed measured by the vehicle speed measuring device islower than a threshold (e.g., an upper-limit vehicle speed VPTMASTH forperforming the driving force assistance using the first motor M1 duringa lock-up mode in the embodiment) which is determined in considerationof efficiencies of the generator and the motor, the control partperforms a low fuel-consumption motor driving-assistance mode (refer tosteps S065 and S066 in the embodiment) in which the motor is selectedfor assisting the driving of the vehicle, and

when the vehicle speed measured by the vehicle speed measuring device ishigher than or equal to the threshold, the control part performs a lowfuel-consumption generator driving-assistance mode (refer to step S068in the embodiment) in which the generator is selected for assisting thedriving of the vehicle.

In this case, the driving force assistance can be effectively performedin consideration of a use-range difference (with respect to the rotationspeed) between the motor and the generator in accordance with theircharacteristics. Therefore, it is possible to minimize the powerconsumption.

In a typical example, the engine can perform a cylinder stop operationin the low fuel-consumption operation mode; and

when the driving of the vehicle is assisted using the motor, the controlpart performs a cylinder stop driving-assistance vibration-control mode(refer to step S066 in the embodiment) in which the generator is drivenfor canceling a vibration of the engine.

In this case, a required driving force to be assisted can be provided bycanceling an engine vibration while the cylinder stop operation ismaintained. Therefore, it is possible to improve the fuel consumption inresponse to the enlarged cylinder stop operation and thus to improve thesalability.

The drive control apparatus may further comprise:

a required driving force measuring device (refer to step S005 in theembodiment) for measuring a required driving force (e.g., a requireddriving force FREQF in the embodiment) of the vehicle, wherein:

when the engine is set in the low fuel-consumption operation mode, thecontrol part performs a low fuel-consumption generator power-generationmode (refer to steps S061 and S062 in the embodiment) in which:

the clutch is connected, and

when the required driving force measured by the required driving forcemeasuring device is less than a predetermined value (e.g., anupper-limit driving force FCYL3 for implementing a cylinder-stopoperation mode in the embodiment), the generator is driven by theengine.

Accordingly, when a relatively small driving force is required, asurplus of the driving force of the engine can be used for generatingelectric power via the generator, thereby improving the fuelconsumption.

In this case, preferably, the engine can perform a cylinder stopoperation in the low fuel-consumption operation mode; and

when the low fuel-consumption generator power-generation mode is active,the control part executes a cylinder stop generator power-generationvibration-control mode (refer to step S062 in the embodiment) in whichthe generator is driven for canceling a vibration of the engine.

Accordingly, the generator can be continuously driven by the engine bycanceling an engine vibration while the cylinder stop operation ismaintained. Therefore, the power generation state using the generatorcan be maintained, thereby improving the fuel consumption.

In this case, the drive control apparatus may further comprise:

an engine speed measuring device (e.g., an engine speed sensor in theembodiment) for measuring an engine speed (e.g., an engine speed NE inthe embodiment) of the engine; and

an intake-pipe negative-pressure measuring device (e.g., an intake-pipenegative-pressure sensor in the embodiment) for measuring an intake-pipenegative pressure (e.g., an intake-pipe negative pressure PB in theembodiment), wherein:

the control part determines whether the generator is driven forcanceling the vibration of the engine based on results of measurementsby the engine speed measuring device and the intake-pipenegative-pressure measuring device (refer to steps S059 and S060 in theembodiment).

Accordingly, it is possible to maximize a cylinder stop operation areawhich is restricted by the engine speed and the intake-pipe negativepressure, and thus to improve the fuel consumption in response to theenlarged cylinder stop operation area.

The present invention also provides a drive control apparatus for ahybrid vehicle, wherein:

the hybrid vehicle comprises:

an engine which can perform a cylinder stop operation;

a generator selectively used for one of being driven by the engine andassisting driving of the engine;

a motor for generating a driving force of the vehicle by electric powersupplied by the generator or a battery device; and

a clutch provided between the generator and wheels of the vehicle, and

the drive control apparatus comprises:

a required driving force measuring device for measuring a requireddriving force of the vehicle;

an operation mode switching device (refer to steps S054, S055, and S056in the embodiment) for selecting, when the clutch is connected, one of:

-   -   a cylinder stop operation mode (refer to steps S061, S062, S065,        S066, and S068 in the embodiment) for performing the cylinder        stop operation,    -   a cylinder stop driving-assistance mode (refer to steps S065,        S066, and S068 in the embodiment), which belongs to the cylinder        stop operation mode, and in which driving of the vehicle is        assisted using one of the generator and the motor, and    -   a full-cylinder operation mode (refer to steps S058, S069, and        S070 in the embodiment) in which no cylinder is stopped,

where the selection is performed based on the required driving force;

a vehicle speed measuring device for measuring a vehicle speed of thevehicle;

a selection device (refer to steps S057 and S067 in the embodiment) forselecting, when one of the cylinder stop driving-assistance mode and thefull-cylinder operation mode is selected by the operation mode switchingdevice, one of the generator and the motor for assisting the driving ofthe vehicle, based on the vehicle speed measured by the engine speedmeasuring device;

an engine speed measuring device for measuring an engine speed of theengine;

an intake-pipe negative-pressure measuring device for measuring anintake-pipe negative pressure; and

a vibration control determination device (refer to steps S059, S060,S063, and S064 in the embodiment) for determining, when one of thecylinder stop operation mode and the cylinder stop driving-assistancemode is selected by the operation mode switching device, whether thegenerator is driven for canceling a vibration of the engine based on theengine speed and the intake-pipe negative pressure.

In accordance with the above structure, (i) the operation mode can beswitched actively, (ii) one of the motor and the generator, which ismore efficient, can be selected for assisting the driving force of theengine, and (iii) the generator can be driven for the engine-vibrationcontrol (when necessary) so as to enlarge the cylinder-stop operationarea. Therefore, it is possible to considerably improve the fuelconsumption.

The above drive control apparatus may further comprise:

a required driving force measuring device for measuring a requireddriving force of the vehicle; and

a vehicle speed measuring device for measuring a vehicle speed of thevehicle, wherein:

when the vehicle speed measured by the required driving force measuringdevice is lower than or equal to a predetermined value (e.g., “NO” instep S008 in the embodiment, wherein the predetermined value is alock-up clutch fastening lower-limit vehicle speed VPLC for fasteningthe clutch in the embodiment), and the required driving force measuredby the required driving force measuring device is larger than or equalto a predetermined value (e.g., “NO” in step S007 in the embodiment,wherein the predetermined value is zero), the control part performs anEV mode (refer to steps S036, S038, and S039 in the embodiment) in whichthe clutch is disconnected and the driving force of the vehicle isgenerated by the motor.

In accordance with the EV mode in which the fuel consumption is reduced(may be zero) by the engine, it is possible to improve the fuelconsumption.

The above-described preferable example of the drive control apparatusmay further comprise:

a required output power measuring device (refer to step S006 in theembodiment) for measuring required output power (e.g., required outputpower PREQ in the embodiment) of the vehicle, wherein:

when the required output power measured by the required output powermeasuring device is higher than an upper-limit output power threshold(e.g., an upper-limit driving output PREQLMT for a BATT EV mode in theembodiment) which is set based on an amount of remaining power of thebattery device (refer to step S032 in the embodiment),

-   -   if the amount of remaining power of the battery device is larger        than or equal to a threshold for forced charging (e.g., “NO” in        step S037 in the embodiment, wherein the threshold is a        lower-limit SOCCHG of remaining power for performing a forced        charging operation in the embodiment), the control part performs        an E-PASS EV mode (refer to step S038 in the embodiment) in        which the generator is driven by the engine, and electric power        generated by the generator is supplied to the motor, and    -   if the amount of remaining power of the battery device is less        than the threshold for forced charging (e.g., “YES” in step S037        in the embodiment), the control part performs a CHRGE EV mode        (refer to step S036 in the embodiment) in which the generator is        driven by the engine, and electric power generated by the        generator is supplied to the storage device and the motor.

In accordance with the E-PASS EV mode, the engine can be efficientlydriven, so as to effectively perform an EV running operation.Additionally, in accordance with the CHRGE EV mode, the battery devicecan be charged in addition to the operation in the E-PASS EV mode.

The above-described preferable example of the drive control apparatusmay also further comprise:

a vehicle speed measuring device for measuring a vehicle speed of thevehicle; and

a required driving force measuring device for measuring a requireddriving force of the vehicle, wherein:

when the required driving force measured by the required driving forcemeasuring device is smaller than zero (e.g., “YES” in step S007 in theembodiment),

-   -   if the clutch is disconnected (e.g., “NO” in step S027 in the        embodiment), the control part performs an S-REGEN mode (refer to        step S029 in the embodiment) in which regeneration of electric        power is performed using the motor,    -   if the clutch is connected (e.g., “YES” in step S027 in the        embodiment) and the vehicle speed measured by the vehicle speed        measuring device is lower than a predetermined value (e.g.,        “YES” in step S028 in the embodiment, wherein the predetermined        value is a lock-up clutch fastening lower-limit vehicle speed        VPDECLCL defined for deceleration), then the control part        performs a cylinder stop lock-up S-REGEN mode (refer to step        S030 in the embodiment) in which the engine performs the        cylinder stop operation and regeneration of electric power is        performed using the generator, and    -   if the clutch is connected and the vehicle speed measured by the        vehicle speed measuring device is higher than or equal to the        predetermined value (e.g., “NO” in step S028 in the embodiment,        wherein the predetermined value is the above lock-up clutch        fastening lower-limit vehicle speed VPDECLCL), then the control        part performs a cylinder stop lock-up P-REGEN mode (refer to        step S031 in the embodiment) in which the engine performs the        cylinder stop operation and regeneration of electric power is        performed using the motor.

In accordance with the S-REGEN mode, energy can be effectively providedto the battery device or “12V consumers” without being affected by apumping loss of the engine. In addition, one of the motor of thegenerator, which can efficiently generate electric power, can beselected by switching the mode between the cylinder stop lock-up S-REGENmode and the cylinder stop lock-up P-REGEN mode in accordance with thevehicle speed. Therefore, electric power can be efficiently generated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the general structure of a hybridvehicle with respect to an embodiment of the present invention.

FIG. 2 is a schematic diagram explaining a start (initial starting)mode.

FIG. 3 is a schematic diagram explaining a start (EV starting) mode.

FIG. 4 is a schematic diagram explaining an E-PASS EV mode.

FIG. 5 is a schematic diagram explaining a BATT EV mode.

FIG. 6 is a schematic diagram explaining an S-REGEN mode.

FIG. 7 is a schematic diagram explaining a CHARGE EV mode.

FIG. 8 is a schematic diagram explaining an IDLE stop mode.

FIG. 9 is a schematic diagram explaining an IDLE mode.

FIG. 10 is a schematic diagram explaining a V6 lock-up mode.

FIG. 11 is a schematic diagram explaining a V6 lock-up P-ASSIST mode.

FIG. 12 is a schematic diagram explaining a cylinder stop lock-up mode.

FIG. 13 is a schematic diagram explaining a cylinder stop lock-upP-ASSIST mode.

FIG. 14 is a schematic diagram explaining a cylinder stop lock-up+ANVmode.

FIG. 15 is a schematic diagram explaining a V6 lock-up S-ASSIST mode.

FIG. 16 is a schematic diagram explaining a cylinder stop lock-upS-ASSIST mode.

FIG. 17 is a schematic diagram explaining a cylinder stop lock-upS-ASSIST+ANV mode.

FIG. 18 is a schematic diagram explaining a cylinder stop lock-upS-REGEN mode.

FIG. 19 is a schematic diagram explaining a cylinder stop lock-upP-REGEN mode.

FIG. 20 is a flowchart for determining the operation.

FIG. 21 is also a flowchart for determining the operation.

FIG. 22 is a flowchart of a process of selecting a mode in the lock-upparallel mode.

FIG. 23 is a chart showing a relationship between the driving force andthe vehicle speed.

FIG. 24 is a chart showing a relationship between the intake-pipenegative pressure and the engine speed.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment in accordance with the present invention willbe described with reference to the appended figures.

FIG. 1 shows the structure of a hybrid vehicle with respect to anembodiment of the present invention. This hybrid vehicle can run usingonly a first motor M1. A second motor M2 is coupled with a crank shaftof a V6 cylinder engine E. A speed change gear box G is connected to thesecond motor M2 via a clutch C.

The speed change box G is, for example, a 5-speed gear box, andtransmits a driving force to right and left driving (front or rear)wheels W of the vehicle via a final gear and a differential gear D fordistributing the driving force between the right and left driving wheelsW. The first motor M1 cooperates with the final gear, and transmitspower via the final gear and the differential gear D, to the drivingwheels W.

The first motor M1 and the second motor M2 each may be a three-phase DCbrushless motor, and are connected to a power drive unit PDU. To eachpower drive unit PDU, a high-voltage Li-ion battery LB is connected,which sends and receives electrical energy to and from the correspondingmotor (M1 or M2).

In a control operation explained below, the first motor M1 and thesecond motor M2 are set in a manner such that their operation rangesoverlap at around 3000 rpm, which is known as the most efficient speedof the motor, and both motors can operate within a range defined aroundthe overlapped area. The active motor (i.e., which is presently used) isselected mainly in accordance with a vehicle speed VP (a speed of thevehicle). More specifically, a motor system is constructed in a mannersuch that the first motor M1 is highly efficient in a relatively lowvehicle-speed range while the second motor M2 is highly efficient in arelatively high vehicle-speed range.

The driving and regenerating operation of each of the motors M1 and M2is performed by the corresponding power drive unit PDU which receives acontrol command issued by a control part 1. For example, in order todrive the first motor M1, the power drive unit PDU converts DC (directcurrent) electric power, which is output from the battery LB, tothree-phase AC (alternating current) electric power, and supplies thepower to the first motor M1, in accordance with a torque command issuedby the control part 1. In order to perform regeneration via the firstmotor M1, the power drive unit PDU converts the three-phase AC electricpower, which is supplied from the first motor ML to DC electric power,and charges the battery LB with the DC electric power.

A 12V auxiliary battery “12V BATT” for driving various accessories(which function as “12V consumers”) is connected in parallel to eachpower drive unit PDU and the battery LB via a so-called “downverter” DBwhich is a DC-DC converter. The downverter DB, controlled by the controlpart 1, charges the 12V auxiliary battery “12V BATT” by dropping thevoltage of each power drive unit PDU or the battery LB.

As described above, the engine E is a V6 cylinder engine, and it has twobanks. Three cylinders belong to one of the banks, and each of the threecylinders has a hydraulic variable-timing valve mechanism VT whichenables a cylinder stop (or idle) operation. The other three cylindersbelong to the other bank, and each of the three cylinders has anordinary valve operation mechanism (not shown) which performs nocylinder stop operation. In the present embodiment, each of the threecylinders (which enable the cylinder stop operation) performs thecylinder stop operation using two intake valves and two exhaust valves,all of which maintain a closed state via the corresponding hydraulicvariable-timing valve mechanism VT.

Accordingly, the operation of the engine E is switched between athree-cylinder operation (i.e., a cylinder stop operation or a lowfuel-consumption mode) in which the three cylinders belonging to saidone of the banks are stopped, and a six-cylinder operation (i.e., a V6operation or a normal fuel-consumption mode) in which all of the sixcylinders belonging to both banks are active.

In addition, a vibration of the engine E, which is generated when theengine E operates in the three-cylinder operation (i.e., cylinder stopoperation), is cancelled by using the second motor M2. It is of coursepossible to further provide an active engine mount for suppressing avibration of the vehicle body.

The engine E has an electronic control throttle 20 for electronicallycontrolling a throttle valve (not shown).

The electronic control throttle 20 directly controls the throttle valvein accordance with a degree of opening of the throttle valve, which iscalculated by the control part 1 based on, for example, anaccelerator-pedal opening degree AP corresponding to the degree ofdepression of an accelerator pedal (not shown) by the driver of thevehicle, the driving state of the vehicle such as the vehicle speed VPor an engine (rotation) speed NE of the engine E, and a torquedistribution state between the engine E and the first motor M1 or thesecond motor M2.

To the control part 1, signals output from the following devices areinput, such as (i) a vehicle speed sensor for measuring the vehiclespeed VP, (ii) an engine water temperature sensor for measuring atemperature of water for the engine E (i.e., engine water temperatureTW), (iii) a catalyst temperature sensor for measuring a catalysttemperature CAT, (iv) an engine speed sensor for measuring the enginespeed NE, (v) a shift position sensor for detecting each shift positionsuch as a front gear F, a rear gear R, a parking gear P, or a neutralgear N, (vi) a brake switch for determining the operation state of abrake pedal BR, (vii) an accelerator pedal opening-degree sensor formeasuring the accelerator-pedal opening degree AP corresponding to thedegree of depression of the accelerator pedal, (viii) a throttleopening-degree sensor for measuring a throttle opening degree TH, (ix)an intake-pipe negative-pressure sensor for measuring an intake-pipenegative pressure PB, (x) a battery temperature sensor for measuring atemperature TBAT of the battery LB, and (xi) a POIL sensor for measuringan oil pressure of a side where the cylinder stop operation is releasedwhile the cylinder stop operation is performed, and the like.

The control part 1 includes: (i) a MOT1 ECU (electronic control unit) 21for controlling the driving and regenerating operation of the firstmotor M1 via the corresponding power drive unit PDU, (ii) a MOT2 ECU 22for controlling the driving and regenerating operation of the secondmotor M2 via the corresponding power drive unit PDU, (iii) a BRAKE ECU23 for controlling a brake device so as to stabilize the movement of thevehicle, (iv) an MG/BAT ECU 24 for monitoring and protecting ahigh-voltage electrical equipment system which may include the powerdrive unit PDUs, the battery LB, the downverter DV, the first motor M1,and the second motor M2, and controlling the operation of the powerdrive unit PDUs and the downverter DV, and (v) an FI ECU 25 forcontrolling the fuel supply to the engine E, the ignition timing, andthe like. The above ECUs 21 to 25 are connected to a meter 26 whichincludes instruments for showing various state quantities.

The operation modes of the present embodiment will be explained withreference to FIGS. 2 to 19.

The present hybrid vehicle has two general modes: one is active when theclutch C is connected (i.e., ON), that is, in a lock-up state (in whichthe crank shaft of the engine E and the speed change box G are directlycoupled via the second motor M2), and the other is active when theclutch C is disconnected (i.e., OFF).

In addition to the state of the clutch C, the operation mode is switchedbetween various modes, in accordance with:

(i) whether the engine E is (a) in the full-cylinder operation (i.e., V6operation) mode, (b) in the three-cylinder operation (i.e., cylinderstop) mode, or (c) stopped,(ii) whether the first motor M1 is (a) generating a driving force, (b)generating electric power while the engine is stopped (i.e., in theregeneration mode), (c) generating electric power while the engineoperates, (d) stopping, or (e) rotating, where the generated torque iszero,(iii) whether the second motor M2 is (a) generating a driving force, (b)generating electric power while the engine is stopped (i.e., in theregeneration mode), (c) generating electric power while the engineoperates, (a) stopping, (e) rotating, where the generated torque iszero, or (f) in a vibration control mode (called “ANV”), or(iv) whether the battery LB is (a) discharging, (b) charging, or (c) ina zero battery-end state (i.e., not discharging nor charging) whichincludes using the battery LB by alternating the charging anddischarging so as to drive the second motor M2 in the vibration controlmode.

FIG. 2 shows a START (or initial starting) mode. In this operation mode,the clutch C is disconnected, the engine E is stopped, the first motorM1 is stopped, the second motor M2 is generating a driving force, andthe battery LB is discharging. That is, the engine E is started when thevehicle stands completely still. When the vehicle is started byswitching an ignition key (or switch) on, electric power is suppliedfrom the battery LB so as to drive the second motor M2 and start theengine E, and simultaneously, electric power is supplied via thedownverter DV to the above-described 12V consumers and the 12V auxiliarybattery “12V BATT”.

FIG. 3 shows a START (EV starting) mode. In this operation mode, theclutch C is disconnected, the engine E is stopped, the first motor M1and the second motor M2 each are generating a driving force, and thebattery LB is discharging. That is, when the clutch C is disconnected,the engine E is stopped, and the vehicle runs using the first motor M1,electric power is supplied from the battery LB so as to drive the secondmotor M2 and to start the engine E, and simultaneously, electric poweris supplied via the downverter DV to the above-described 12V consumersand the 12V auxiliary battery “12V BATT”.

FIG. 4 shows an E-PASS EV mode. In this operation mode, the clutch C isdisconnected, the engine E operates in the V6 operation mode, the firstmotor M1 is generating a driving force, the second motor M2 isgenerating electric power, and the battery LB is in the zero battery-endstate. That is, the vehicle runs by driving the first motor M1 by usingthe electric power generated by the second motor M2, and simultaneously,electric power is supplied via the downverter DV to the above-described12V consumers and the 12V auxiliary battery “12V BATT”.

If the reverse position R is detected by the shift position sensor, thefirst motor M1 is reversely rotated so that the vehicle moves backward(i.e., in an E-PASS EV REVERSE mode).

FIG. 5 shows a BATT EV mode. In this operation mode, the clutch C isdisconnected, the engine E is stopped, the first motor M1 is generatinga driving force, the second motor M2 is stopped, and the battery LB isdischarging. This mode is used when, for example, the efficiency ofelectric power generation is low, and in this mode, the vehicle runs bydriving the first motor M1 by only using the electric power supplied bythe battery LB.

When the reverse position R is detected by the shift position sensor andthe first motor M1 is reversely rotated, the vehicle moves backward(i.e., in a BATT EV REVERSE mode).

FIG. 6 shows an S-REGEN mode. In this operation mode, the clutch C isdisconnected, the engine E is stopped, the first motor M1 is generatingelectric power (i.e., in the regeneration mode), the second motor M2 isstopped, and the battery LB is charging. That is, regeneration isperformed using the first motor M1 while the vehicle is decelerated, andelectric power is supplied via the battery LB and the downverter DV tothe above-described 12V consumers and the 12V auxiliary battery “12VBATT”. In this mode, it is possible to obtain a maximum quantity ofregeneration by omitting resistance due to the operation of the engine Eor the second motor M2. Here, “S” in the S-REGEN mode is an abbreviationof “series”, and indicates that the first motor M1 participates in theoperation. In addition, “REGEN” indicates regeneration.

FIG. 7 shows a CHARGE EV mode. In this operation mode, the clutch C isdisconnected, the engine E operates in the V6 operation mode, the firstmotor M1 is generating a driving force, the second motor M2 isgenerating electric power, and the battery LB is charging. That is, thesecond motor M2 generates electric power by which the vehicle runs viathe first motor M1 and the battery LB is charged, and the electric poweris also supplied via the downverter DV to the above-described 12Vconsumers and the 12V auxiliary battery “12V BATT”.

FIG. 8 shows an IDLE stop mode. In this operation mode, the clutch C isdisconnected, the engine E is stopped, the first motor M1 is stopped,the second motor M2 is also stopped, and the battery LB is discharging.That is, electric power is supplied from the battery LB via thedownverter DV to the above-described 12V consumers and the 12V auxiliarybattery “12V BATT”.

FIG. 9 shows an IDLE mode. In this operation mode, the clutch C isdisconnected, the engine E operates in the V6 operation mode, the firstmotor M1 is stopped, the second motor M2 is generating electric power,and the battery LB is in the zero battery-end state. That is, the secondmotor M2 generates electric power which is supplied via the downverterDV to the above-described 12V consumers and the 12V auxiliary battery“12V BATT”.

FIG. 10 shows a V6 lock-up mode. In this operation mode, the clutch C isconnected, the engine E operates in the V6 operation mode, the firstmotor M1 is rotating while the generated torque is zero, the secondmotor M2 is generating electric power, and the battery LB is in the zerobattery-end state. That is, the second motor M2 generates electric powerwhich is supplied via the downverter DV to the above-described 12Vconsumers and the 12V auxiliary battery “12V BATT”, and the vehicle runsby the engine E.

FIG. 11 shows a V6 lock-up P-ASSIST mode. In this operation mode, theclutch C is connected, the engine E operates in the V6 operation mode,the first motor M1 is rotating while the generated torque is zero, thesecond motor M2 is generating a driving force, and the battery LB isdischarging. That is, when a load of the vehicle slightly increaseswhile the vehicle runs in the V6 lock-up mode, driving force of theengine E is assisted by the second motor M2 using the electric powersupplied from the battery LB, and simultaneously, the electric powerfrom the battery LB is supplied via the downverter DV to theabove-described 12V consumers and the 12V auxiliary battery “12V BATT”,so that the vehicle runs. Here, “P” in “P-ASSIST” is an abbreviation of“parallel”, and indicates that the second motor M2 participates in theoperation, and “ASSIST” indicates the above assistance.

FIG. 12 shows a cylinder stop lock-up mode. In this operation mode, theclutch C is connected, the engine E operates in the cylinder stop mode,the first motor M1 is rotating while the generated torque is zero, thesecond motor M2 is generating electric power, and the battery LB is inthe zero battery-end state. That is, when the load of the vehicledecreases while the vehicle runs in the V6 lock-up mode, the engine E isoperated in the cylinder stop mode, and the electric power generated bythe second motor M2 is supplied via the downverter DV to theabove-described 12V consumers and the 12V auxiliary battery “12V BATT”,so that the vehicle runs using the engine E.

FIG. 13 shows a cylinder stop lock-up P-ASSIST mode. In this operationmode, the clutch C is connected, the engine E operates in the cylinderstop mode, the first motor M1 is rotating while the generated torque iszero, the second motor M2 is generating a driving force, and the batteryLB is discharging. That is, when the load of the vehicle slightlyincreases while the vehicle runs in the cylinder stop lock-up mode, itis determined whether the engine E can be assisted while the cylinderstop operation is continued. If it can, driving force of the engine E,which is still in the cylinder stop mode, is assisted by the secondmotor M2 using the electric power from the battery LB, which is alsosupplied via the downverter DV to the above-described 12V consumers andthe 12V auxiliary battery “12V BATT”, so that the vehicle runs.

FIG. 14 shows a cylinder stop lock-up+ANV mode. In this operation mode,the clutch C is connected, the engine E operates in the cylinder stopmode, the first motor M1 is rotating while the generated torque is zero,the second motor M2 is in the vibration control mode, and the battery LBis in the zero battery-end state. That is, part of the electric powergenerated by the second motor M2 is supplied via the downverter DV tothe above-described 12V consumers and the 12V auxiliary battery “12VBATT”, and simultaneously, a driving force generated by the second motorM2 is used for controlling and canceling a vibration (or noise) of theengine E, which is caused by the cylinder-stop operation. In this case,as shown by dashed arrows in FIG. 14, the first motor M1 may be drivenusing part of the electric power generated by the second motor M2.Additionally, “ANV” indicates vibration control.

FIG. 15 shows a V6 lock-up S-ASSIST mode. In this operation mode, theclutch C is connected, the engine E operates in the V6 operation mode,the first motor M1 is generating a driving force, the second motor M2 isrotating while the generated torque is zero, and the battery LB isdischarging. That is, when the load of the vehicle increases while thevehicle runs in the V6 operation mode, the first motor M1 is drivenusing the electric power supplied from the battery LB, so as to assistthe driving force of the engine E, and simultaneously, the electricpower from the battery LB is also supplied via the downverter DV to theabove-described 12V consumers and the 12V auxiliary battery “12V BATT”,so that the vehicle runs.

FIG. 16 shows a cylinder stop lock-up S-ASSIST mode. In this operationmode, the clutch C is connected, the engine E operates in the cylinderstop mode, the first motor M1 is generating a driving force, the secondmotor M2 is rotating while the generated torque is zero, and the batteryLB is discharging. That is, when the load of the vehicle slightlyincreases while the vehicle runs in the cylinder stop lock-up mode, itis determined whether the engine E can be assisted while the cylinderstop operation is continued. If it can, driving force of the engine E,which is still in the cylinder stop mode, is assisted by the first motorM1 using the electric power from the battery LB, which is also suppliedvia the downverter DV to the above-described 12V consumers and the 12Vauxiliary battery “12V BATT”, so that the vehicle runs.

FIG. 17 shows a cylinder stop lock-up S-ASSIST+ANV mode. In thisoperation mode, the clutch C is connected, the engine E operates in thecylinder stop mode, the first motor M1 is generating a driving force,the second motor M2 is in the vibration control mode, and the battery LBis discharging. That is, the first motor M1 is driven so as to assistthe driving force of the engine E, and the second motor M2 is used forcontrolling and canceling the vibration of the engine E.

Here, the second motor M2 may be used for performing the driving forceassistance and the vibration control. However, in this case, one of thedriving force assistance and the vibration control is restricted.Therefore, in the present mode, the driving force assistance and thevibration are distributed between the first motor M1 and the secondmotor M2 in the cylinder stop running operation, so that they can beperformed without providing any restriction to each other. Accordingly,a (driving force) assistance range in the cylinder stop operation can beenlarged, so that frequency of mode-shift to the V6 operation isreduced, thereby improving the fuel consumption.

FIG. 18 shows a cylinder stop lock-up S-REGEN mode. In this operationmode, the clutch C is connected, the engine E operates in the cylinderstop mode, the first motor M1 is generating electric power (i.e., in theregeneration mode), the second motor M2 is rotating while the generatedtorque is zero, and the battery LB is charging.

FIG. 19 shows a cylinder stop lock-up P-REGEN mode. In this operationmode, the clutch C is connected, the engine E operates in the cylinderstop mode, the first motor M1 is rotating while the generated torque iszero, the second motor M2 is generating electric power (i.e., in theregeneration mode), and the battery LB is charging.

Below, an operation determination process for determining the operationmode will be explained with reference to a flowchart shown in FIGS. 20and 21.

In the first step S001 it is determined whether the shift position isthe R (reverse) position. When the result of the determination is “YES”,the operation proceeds to step S013, and when it is “NO”, the operationproceeds to step S002.

In step S013, a required driving force FREQR (for the backward movement)is retrieved from a map (i.e., a map search is performed) based on thevehicle speed VP and the accelerator-pedal opening degree AP, and in thefollowing step S014, a required output power PREQ is computed inaccordance with the vehicle speed VP and the required driving forceFREQR (for the backward movement). The operation then proceeds to stepS015.

In step S015, a permissive upper-limit output power PREQLMT for thedriving operation in the BATT EV mode is retrieved from a map, based onan amount of remaining power (called “SOC”) of the battery LB.

In the following step S016, it is determined whether the required outputpower PREQ is higher than the permissive upper-limit output powerPREQLMT. When the result of the determination is “YES”, the operationproceeds to step S019, and when it is “NO”, the operation proceeds tostep S017.

In step S019, the E-PASS EV REVERSE mode (see FIG. 4) is selected, andthe process of the present flowchart is terminated. This mode isselected because no electric power is supplied from the battery LB, andthus the required output power must be obtained by operating the engineE.

In step S017, it is determined whether the engine water temperature TWis higher than a lower-limit engine water temperature TWEV for makingthe vehicle run in the BATT EV mode. When the result of thedetermination is “YES”, the operation proceeds to step S018, and when itis “NO”, the operation proceeds to step S019. The above determination isexecuted because when the engine water temperature TW is low, the engineE should be started. The above lower-limit engine water temperature TWEVhas an identical value to a lower-limit engine water temperature forexecuting the idle stop operation, which is explained later.

In step S018, it is determined whether the catalyst temperature CAT ishigher than a lower-limit catalyst temperature TCATEV for making thevehicle run in the BATT EV mode. When the result of the determination is“YES”, the operation proceeds to step S020, and when it is “NO”, theoperation proceeds to step S019.

In step S020, the BATT EV REVERSE mode (see FIG. 5) is selected, and theprocess of the present flowchart is terminated. This mode is selectedbecause when the catalyst temperature CAT is low, the engine E should bestarted. The above lower-limit catalyst temperature TCATEV has anidentical value to a lower-limit catalyst temperature for executing anidle stop operation, which is explained later.

In step S002, it is determined whether the shift position is the P(parking) or N (neutral) position. When the result of the determinationis “YES”, the operation proceeds to step S021, and when it is “NO”, theoperation proceeds to step S003.

In step S021, it is determined whether the amount SOC of remaining powerof the battery LB is larger than a lower-limit SOCIDLE for executing theidle stop operation. This determination is performed so as to determinewhether the amount SOC is sufficient for executing the idle stopoperation. When the result of the determination in step S021 is “YES”,the operation proceeds to step S022, and when it is “NO”, the operationproceeds to step S024. In step S024, the IDLE mode (see FIG. 9) isselected, and the process of the present flowchart is terminated.

In step S022, it is determined whether the engine water temperature TWis higher than the lower-limit engine water temperature TWEV forexecuting the idle stop operation. When the result of the determinationis “YES”, the operation proceeds to step S023, and when it is “NO”, theoperation proceeds to step S024.

In step S023, it is determined whether the catalyst temperature CAT ishigher than the lower-limit catalyst temperature TCATEV for executingthe idle stop operation. When the result of the determination is “YES”,the operation proceeds to step S025, and when it is “NO”, the operationproceeds to step S024. In step S025, the IDLE stop mode (see FIG. 8) isselected, and the process of the present flowchart is terminated.

In step S003, it is determined whether a braking operation has beenperformed. When the result of the determination is “YES”, the operationproceeds to step S004, and when it is “NO”, the operation proceeds tostep S005.

In step S004, it is determined whether the vehicle speed VP is zero.When the result of the determination is “YES”, the vehicle stands still,and the operation proceeds to step S021. When the result of thedetermination is “NO”, the vehicle is running and the operation proceedsto step S005.

In step S005, a required driving force FREQF (for the forward movement)is retrieved from a map (i.e., a map search is performed) based on thevehicle speed VP and the accelerator-pedal opening degree AP, and in thefollowing step S006, the required output power PREQ is computed inaccordance with the vehicle speed VP and the required driving forceFREQF (for the forward movement). The operation then proceeds to stepS007.

In step S007, it is determined whether the required driving force FREQF(for the forward movement) is less than zero. When the result of thedetermination is “YES” (i.e., in deceleration), the operation proceedsto step S026, and when it is “NO”, the operation proceeds to step S008.

In step S026, it is determined whether the vehicle speed VP is higherthan a lock-up clutch fastening lower-limit vehicle speed VPLC forfastening the clutch C. When the result of the determination is “YES”(i.e., the vehicle speed VP has a value for implementing the lock-upstate), the operation proceeds to step S027, and when it is “NO” (i.e.,the lock-up state cannot be implemented by the vehicle speed VP), theoperation proceeds to step S029.

In step S029, the S-REGEN mode (see FIG. 6) is selected, and the processof the present flowchart is terminated.

In step S027, it is determined whether the lock-up state is active. Whenthe result of the determination is “YES”, the operation proceeds to stepS028, and when it is “NO”, the operation proceeds to step S029. Thisdetermination is performed because in the vehicle having a high vehiclespeed and a disconnected clutch, a larger amount of loss occurs byincreasing the engine speed NE so as to implement the lock-up state, andit is preferable to select the S-REGEN mode (see FIG. 6) in step S029without performing such an operation.

In step S028, it is determined whether the vehicle speed VP is lowerthan a lock-up clutch fastening lower-limit vehicle speed VPDECLCLdefined for deceleration. This determination is performed so as todetermine whether the regeneration should be performed using the firstmotor M1 or the second motor M2, in consideration of the efficiency ofthe motor. When the result of the determination in step S028 is “YES”,the operation proceeds to step S030, and when it is “NO”, the operationproceeds to step S031.

In step S030, the cylinder stop lock-up S-REGEN mode (see FIG. 18) isselected, and the process of the present flowchart is terminated. Instep S031, the cylinder stop lock-up P-REGEN mode (see FIG. 19) isselected, and the process of the present flowchart is terminated. Theabove selection is performed because (i) with respect to the secondmotor M2, the higher the rotation speed (i.e., the vehicle speed), thehigher the efficiency, and (ii) with respect to the first motor M1, thelower the rotation speed (i.e., the vehicle speed), the higher theefficiency.

In step S008, it is determined whether the vehicle speed VP is higherthan the lock-up clutch fastening lower-limit vehicle speed VPLC. Thisdetermination is performed because the lock-up connection cannot beexecuted until the vehicle speed reaches a certain level. Based on thisdetermination, it is determined whether the running (of the vehicle)using the first motor M1 is performed. When the result of thedetermination in step S008 is “YES”, the operation proceeds to stepS009, and when it is “NO”, the operation proceeds to step S032.

In step S009, a lock-up clutch fastening upper-limit driving forceFLCPLT is retrieved from a map based on the vehicle speed VP and theamount SOC of remaining power of the battery LB. This map search isperformed based on a map shown in FIG. 23 in which the horizontal axisindicates the vehicle speed VP (km/h) while the vertical axis indicatesthe driving force (N), and also in consideration of the amount SOC ofremaining power of the battery LB.

As shown in FIG. 23, when the vehicle speed VP is higher than thelock-up clutch fastening lower-limit vehicle speed VPLC, the followingfour limits are defined with respect to the driving force: (i) thelock-up clutch fastening upper-limit driving force FLCPLT (i.e., thelimit for implementing the lock-up connection of the clutch C), (ii) anupper-limit driving force FCYL3A for implementing a cylinder-stopenlarged assistance operation mode (i.e., the limit for the drivingforce assistance with respect to the three-cylinder operation), (iii) anupper-limit driving force FCYL6 for implementing a V6 operation mode(i.e., the limit for the V6 engine), and (iv) an upper-limit drivingforce FCYL3 for implementing a cylinder-stop operation mode (i.e., thelimit for the three-cylinder operation). With respect to a line (shownin FIG. 23) assigned to each of the above limits, a higher-speed areaand a lower-speed area are defined on either side of an upper-limitvehicle speed VPTMASTH for performing the driving force assistance usingthe first motor M1 during the lock-up mode. In the higher-speed area,the driving force assistance is performed using the second motor M2, andin the lower-speed area, the driving force assistance is performed usingthe second motor M1.

The second motor M2 rotates at the same rotation speed as that of theengine E; thus, it is used at a higher rotation speed in comparison withthe first motor M1. Therefore, when the vehicle speed reaches a level(i.e., the upper-limit vehicle speed VPTMASTH for performing the drivingforce assistance using the first motor M1 during the lock-up mode), atwhich the efficiency of the driving force assistance is degraded ifusing the first motor M1, it is preferable to use the second motor M2for the driving force assistance at a higher vehicle speed (i.e., thanVPTMASTH) at which the second motor M2, having a higher rotation speed,has a higher efficiency, and it provides lower loss.

In the next step S010, it is determined whether the required drivingforce FREQF (for the forward movement) is less than the lock-up clutchfastening upper-limit driving force FLCPLT. This determination isperformed because when FREQF is larger than FLCPLT, a shock occurs andthe lock-up connection cannot be performed. When the result of thedetermination is “YES”, the operation proceeds to step S011, and when itis “NO”, the operation proceeds to step S032.

In step S011, a lock-up parallel mode is selected, and in the next stepS012, a process (see FIG. 22) of selecting a mode in the lock-upparallel mode is performed. This process will be explained later.

In step S032, the permissive upper-limit driving output PREQLMT for theBATT EV mode is retrieved from a map (i.e., a map search is performed)based on the amount SOC of remaining power of the battery LB, and theoperation proceeds to step S033.

In step S033, it is determined whether the required output power PREQ ishigher than the upper-limit driving output PREQLMT for the BATT EV mode.This determination is performed so as to determine whether the running(of the vehicle) using only the battery LB is possible. When the resultof the determination in step S033 is “YES”, the operation proceeds tostep S037, and when it is “NO”, the operation proceeds to step S034.

In step S037, it is determined whether the amount SOC of remaining powerof the battery LB is less than a lower-limit SOCCHG of remaining powerfor performing a forced charging operation. When the result of thedetermination is “YES” (i.e., charging is necessary), the operationproceeds to step S036, and when it is “NO” (i.e., charging isunnecessary), the operation proceeds to step S038.

In step S036, the CHARGE EV mode (see FIG. 7) is selected, and theprocess of the present flowchart is terminated.

In step S038, the E-PASS EV mode (see FIG. 4) is selected, and theprocess of the present flowchart is terminated.

In step S034, it is determined whether the engine water temperature TWis higher than the lower-limit engine water temperature TWEV for makingthe vehicle run in the BATT EV mode. When the result of thedetermination is “YES”, the operation proceeds to step S035, and when itis “NO” (i.e., when the engine E should be driven), the operationproceeds to step S037.

In step S035, it is determined whether the catalyst temperature CAT ishigher than the lower-limit catalyst temperature TCATEV for making thevehicle run in the BATT EV mode. When the result of the determination is“YES”, the operation proceeds to step S039, and when it is “NO” (i.e.,when the engine E should be driven), the operation proceeds to stepS037.

In step S039, the BATT EV mode (see FIG. 5) is selected, and the processof the present flowchart is terminated.

Below, the process of selecting a mode in the lock-up parallel mode willbe explained with reference to a flowchart shown in FIG. 22. In theexplanation, each mode to be selected belongs to the lock-up mode, whichis indicated by the term “lock-up” enclosed in brackets. In FIG. 22, theterm “lock-up” is omitted.

In the first step S051, the upper-limit driving force FCYL3 forimplementing the cylinder-stop operation mode is retrieved from a map(i.e., a map search is performed) based on the vehicle speed VP.

In the following step S052, the upper-limit driving force FCYL3A forimplementing the cylinder-stop enlarged assistance operation mode isretrieved from a map based on the vehicle speed VP and the amount SOC ofremaining power of the battery LB.

In the following step S053, the upper-limit driving force FCYL6 forimplementing the V6 operation mode is retrieved from a map based on thevehicle speed VP. The operation then proceeds to step S054.

Each of the above map-search steps is performed based on theabove-described map shown in FIG. 23 in which the horizontal axisindicates the vehicle speed VP (km/h) while the vertical axis indicatesthe driving force (N), and also in consideration of the amount SOC ofremaining power of the battery LB (in case of step S052).

In step S054, it is determined whether the required driving force FREQF(for the forward movement) is less than the upper-limit driving forceFCYL3 for implementing the cylinder-stop operation mode. When the resultof the determination is “YES”, the operation proceeds to step S059, andwhen it is “NO”, the operation proceeds to step S055.

In step S059, it is determined whether the engine speed NE is lower thanan upper-limit engine speed NEANV for performing vibration control. Whenthe result of the determination is “YES”, the operation proceeds to stepS060, and when it is “NO”, the operation proceeds to step S061.

In step S061, the cylinder stop (lock-up) mode (see FIG. 12) isselected, and the process of the present flowchart is terminated.

In step S060, it is determined whether the intake-pipe negative pressurePB belongs to a higher-load range (in which the absolute value of thenegative pressure is relatively large) in comparison with a lower-limitintake-pipe negative pressure PBANV for performing the vibrationcontrol, that is, whether PB is higher than PBANV. When the result ofthe determination is “YES” (i.e., in the higher-load range), theoperation proceeds to step S062, and when it is “NO” (i.e., in alower-load range), the operation proceeds to step S061.

In step S062, the cylinder stop (lock-up)+ANV mode (see FIG. 14) isselected, and the process of the present flowchart is terminated.

FIG. 24 shows a map in which the horizontal axis indicates the enginespeed NE (rpm) while the vertical axis indicates the intake-pipenegative pressure PB (mmHg). The upper-limit engine speed NEANV and thelower-limit intake-pipe negative pressure PBANV for performing thevibration control are defined in this map, and the vibration control isperformed in a vibration control area A (see the hatched area in FIG.24) defined by NEANV and PBANV. That is, in order to enlarge thecylinder-stop operation area without vibration control (i.e., when novibration control is performed), the engine E provides a vibration in anarea (i.e., the vibration control area A in FIG. 24) having a low enginespeed (i.e., lower than the upper-limit engine speed NEANV) and a highload (i.e., having a higher negative pressure than the lower-limitintake-pipe negative pressure PBANV). Therefore, as shown in FIG. 24,the vibration control is effectively performed in this area so as toprovide a cylinder-stop operation area with vibration control, which iswider than the cylinder-stop operation area without vibration control.

In step S055, it is determined whether the required driving force FREQF(for the forward movement) is less than the upper-limit driving forceFCYL3A for implementing the cylinder-stop enlarged assistance operationmode. When the result of the determination is “YES”, the operationproceeds to step S067, and when it is “NO”, the operation proceeds tostep S056.

In step S067, it is determined whether the vehicle speed VP is lowerthan the upper-limit vehicle speed VPTMASTH for performing the drivingforce assistance using the first motor M1 during the lock-up mode. Whenthe result of the determination is “YES”, the operation proceeds to stepS063, and when it is “NO”, the operation proceeds to step S068.

In step S068, the cylinder stop (lock-up) P-ASSIST mode (see FIG. 13) isselected so as to perform the driving force assistance using the secondmotor M2 while the cylinder-stop operation is performed. The process ofthe present flowchart is then terminated.

In step S063, it is determined whether the engine speed NE is lower thanthe upper-limit engine speed NEANV for performing the vibration control.When the result of the determination is “YES”, the operation proceeds tostep S064, and when it is “NO”, the operation proceeds to step S065.

In step S065, the cylinder stop (lock-up) S-ASSIST mode (see FIG. 16) isselected so as to perform the driving force assistance using the firstmotor M1 while the cylinder-stop operation is performed. The process ofthe present flowchart is then terminated.

In step S064, it is determined whether the intake-pipe negative pressurePB belongs to the higher-load range (in which the absolute value of thenegative pressure is relatively large) in comparison with thelower-limit intake-pipe negative pressure PBANV for performing thevibration control, that is, whether PB is higher than PBANV.

When the result of the determination is “YES” (i.e., in the higher-loadrange), the operation proceeds to step S066, and when it is “NO” (i.e.,in the lower-load range), the operation proceeds to step S065.

In step S066, the cylinder stop (lock-up) S-ASSIST+ANV mode (see FIG.17) is selected so as to perform (i) the driving force assistance usingthe first motor M1 and (ii) the vibration control using the second motorM2, while the cylinder-stop operation is performed. The process of thepresent flowchart is then terminated.

In step S056, it is determined whether the required driving force FREQF(for the forward movement) is less than the upper-limit driving forceFCYL6 for implementing the V6 operation mode. When the result of thedetermination is “YES”, the operation proceeds to step S070, and when itis “NO”, the operation proceeds to step S057.

In step S070, the V6 (lock-up) mode (see FIG. 10) is selected, and theprocess of the present flowchart is terminated.

In step S057, it is determined whether the vehicle speed VP is lowerthan the upper-limit vehicle speed VPTMASTH for performing the drivingforce assistance using the first motor M1 during the lock-up mode. Whenthe result of the determination is “YES”, the operation proceeds to stepS058, and when it is “NO”, the operation proceeds to step S069.

In step S058, the V6 (lock-up) S-ASSIST mode (see FIG. 15) forperforming the driving force assistance using the first motor M1 isselected, and the process of the present flowchart is terminated.

In step S069, the V6 (lock-up) P-ASSIST mode (see FIG. 11) forperforming the driving force assistance using the second motor M2 isselected, and the process of the present flowchart is terminated.

In accordance with the above-described embodiment, in step S067, it isdetermined whether the vehicle speed VP is lower than the upper-limitvehicle speed VPTMASTH for performing the driving force assistance usingthe first motor M1 during the lock-up mode, and when the vehicle speedVP is higher than or equal to the upper-limit vehicle speed VPTMASTH,the cylinder stop (lock-up) P-ASSIST mode (see FIG. 13) is selected instep S068 so as to perform the driving force assistance using the secondmotor M2. In contrast, when the vehicle speed VP is lower than theupper-limit vehicle speed VPTMASTH, if the engine speed is high or theload is low (i.e., “NO” in step S063 or S064), by which no enginevibration occurs, then the cylinder stop (lock-up) S-ASSIST mode (seeFIG. 16) is selected in step S065 so as to perform the driving forceassistance using the first motor M1.

Therefore, the driving force assistance can be effectively performedusing one of the first motor M1 and the second motor M2 during thecylinder stop operation for reducing the fuel consumption. That is, ause-range (or area) difference between both motors is considered, morespecifically, in a higher vehicle-speed area with respect to theupper-limit vehicle speed VPTMASTH for performing the driving forceassistance using the first motor M1, the second motor M2 is used, and ina lower vehicle-speed area with respect to VPTMASTH, the first motor M1is used, thereby reducing a loss. Accordingly, the electric powerconsumption can be minimized while a required driving force is provided,so that the fuel consumption can be further improved, thereby alsoimproving salability

In addition, when the vehicle speed VP is lower than the upper-limitvehicle speed VPTMASTH, if the engine speed is low and the load is high,which causes an engine vibration due to an unbalanced state during thecylinder stop operation, then the cylinder stop lock-up S-ASSIST+ANVmode is selected so as to perform (i) the driving force assistance usingthe first motor M1 and (ii) the vibration control using the second motorM2 so as to cancel the vibration.

Therefore, the above vibration control satisfies a request for thedriving force assistance while maintaining a low fuel-consumption stateobtained by the cylinder stop operation. Such an enlarged cylinder-stopoperation can improve the fuel consumption, thereby providing preferablesalability.

In particular, the driving force assistance can be performed only usingthe first motor M1 while the driving force of the second motor M2 can beused only for the vibration control; thus, both the vibration controland the driving force assistance can be performed without providing anundesirable influence on each other. That is, if the second motor M2 isused for both the vibration control and the driving force assistance,the amount of driving force for assistance is restricted due to thevibration control. Such a restriction does not occur in the presentembodiment.

If, in step S054, the required driving force FREQF (for the forwardmovement) is less than the upper-limit driving force FCYL3 forimplementing the cylinder-stop operation mode (i.e., “YES” in stepS054), then a cylinder stop (lock-up) mode is selected in step S061 orS062 in which the engine E is operated in the cylinder stop mode whilethe clutch C is connected (i.e., in the lock-up state, selected when“YES” in step S010), so that the vehicle runs while generating electricpower by the second motor M2 which is driven by the engine E. Therefore,when a relatively small driving force FREQF (for the forward movement)is required, a surplus of the driving force of the engine E can be usedfor generating electric power via the second motor M2, thereby improvingthe fuel consumption.

In this case, if the engine E has a low engine speed and the load ishigh, an engine vibration occurs, which can be cancelled using thecylinder stop (lock-up)+ANV mode (see step S062) for performing thevibration control by driving the second motor M2 so as to maintain thecylinder stop operation. Therefore, it is possible to maintain thecylinder stop operation by canceling the engine vibration while thesecond motor M2 is continuously driven by the engine E. Accordingly,electric power generation using the second motor M2 can be continuouslyperformed, thereby improving the fuel consumption.

In addition, as shown in FIG. 24, no vibration occurs in the engine Ewhen only one of the following conditions is satisfied during thecylinder stop (lock-up) operation: (i) the engine speed NE is lower thanthe upper-limit engine speed NEANV for performing the vibration control(i.e., “YES” in step S059 or S063), and (ii) the intake-pipe negativepressure PB belongs to a higher-load range (in which the absolute valueof the negative pressure is relatively large) in comparison with thelower-limit intake-pipe negative pressure PBANV for performing thevibration control (i.e., “YES” in step S060 or S064). Therefore, in thiscase, the cylinder stop operation can be maintained. However, if both ofthe above conditions are satisfied, an engine vibration is inevitable,and the cylinder stop operation cannot be maintained.

Accordingly, the engine speed NE and the intake-pipe negative pressurePB are monitored so as to determine whether the second motor M2 isdriven for the vibration control. The second motor M2 is driven for thevibration control only when both the above conditions are satisfied (seesteps S062 and S066). Therefore, it is possible to maximize the cylinderstop operation area which is restricted by the engine speed NE and theintake-pipe negative pressure PB, and thus to improve the fuelconsumption in response to the enlarged cylinder stop operation area.

As described above, (i) the operation mode is switched actively, inparticular, in accordance with the required driving force FREQF (for theforward movement), (ii) one of the first motor M1 and the second motorM2, which is more efficient, can be selected for assisting the drivingforce of the engine E, and (iii) the second motor M2 can be driven forthe vibration control (when necessary) so as to enlarge thecylinder-stop operation area. Therefore, it is possible to considerablyimprove the fuel consumption.

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as being limited bythe foregoing description, and is only limited by the scope of theappended claims.

For example, the above embodiment employs an engine having acylinder-stop operation mode as the low fuel-consumption operation mode.However, the present invention can also be applied to a vehicle havingan engine which can perform a lean-burn operation or an HCCI operation(in which a gasoline engine performs self ignition by direct jetting).

Also in the above embodiment, the speed change box is a 5-speed gearbox; however, it may also be a 6-speed gear box.

Also in the above embodiment, the engine has six cylinders and three ofthem can be stopped in the cylinder stop operation. However, the presentinvention can also be applied to a vehicle having any engine which canperform a cylinder stop operation, for example, an engine having fourcylinders in which one or two cylinders are stopped in the cylinder stopoperation.

In a variation of the above embodiment, front wheels are driven usingthe engine E and the second motor M2 while rear wheels are driven usingthe first motor M1.

In addition, the battery device is not limited to the battery LB, andthe present invention can also be applied to a vehicle having acapacitor as the battery device.

1-11. (canceled)
 12. A drive control apparatus for a hybrid vehicle,wherein: the hybrid vehicle comprises: an engine which is selectivelyset in one of a normal fuel-consumption operation mode and a lowfuel-consumption operation mode for obtaining a lower fuel consumptionin comparison with the normal fuel-consumption operation mode; agenerator selectively used for one of being driven by the engine andassisting driving of the engine; a motor for generating a driving forceof the vehicle by electric power supplied by the generator or a batterydevice; and a clutch provided between the generator and wheels of thevehicle, and the drive control apparatus comprises: a control part forperforming a low fuel-consumption driving assistance mode when theengine is set in the low fuel-consumption operation mode, wherein in thelow fuel-consumption driving assistance mode: the clutch is connected;and driving of the vehicle is assisted using one of the generator andthe motor, which is selected in accordance with an operation state ofthe vehicle; a vehicle speed measuring device for measuring a vehiclespeed of the vehicle, wherein: when the vehicle speed measured by thevehicle speed measuring device is lower than a threshold which isdetermined in consideration of efficiencies of the generator and themotor, the control part performs a low fuel-consumption motordriving-assistance mode in which the motor is selected for assisting thedriving of the vehicle, and when the vehicle speed measured by thevehicle speed measuring device is higher than or equal to the threshold,the control part performs a low fuel-consumption generatordriving-assistance mode in which the generator is selected for assistingthe driving of the vehicle; a vehicle speed measuring device formeasuring a vehicle speed of the vehicle; and a required driving forcemeasuring device for measuring a required driving force of the vehicle,wherein: when the required driving force measured by the requireddriving force measuring device is smaller than zero, if the clutch isdisconnected, the control part performs an S-REGEN mode in whichregeneration of electric power is performed using the motor, if theclutch is connected and the vehicle speed measured by the vehicle speedmeasuring device is lower than a predetermined value, then the controlpart performs a cylinder stop lock-up S-REGEN mode in which the engineperforms the cylinder stop operation and regeneration of electric poweris performed using the generator, and if the clutch is connected and thevehicle speed measured by the vehicle speed measuring device is higherthan or equal to the predetermined value, then the control part performsa cylinder stop lock-up P-REGEN mode in which the engine performs thecylinder stop operation and regeneration of electric power is performedusing the motor.
 13. The drive control apparatus in accordance withclaim 12, wherein when one of the generator and the motor is selected,one having a higher efficiency is selected.
 14. The drive controlapparatus in accordance with claim 12, wherein: the engine is capable ofperforming a cylinder stop operation in the low fuel-consumptionoperation mode; and when the driving of the vehicle is assisted usingthe motor, the control part performs a cylinder stop driving-assistancevibration-control mode in which the generator is driven for canceling avibration of the engine.
 15. The drive control apparatus in accordancewith claim 12, further comprising: a required driving force measuringdevice for measuring a required driving force of the vehicle, wherein:when the engine is set in the low fuel-consumption operation mode, thecontrol part performs a low fuel-consumption generator power-generationmode in which: the clutch is connected, and when the required drivingforce measured by the required driving force measuring device is lessthan a predetermined value, the generator is driven by the engine. 16.The drive control apparatus in accordance with claim 15, wherein: theengine is capable of performing a cylinder stop operation in the lowfuel-consumption operation mode; and when the low fuel-consumptiongenerator power-generation mode is active, the control part executes acylinder stop generator power-generation vibration-control mode in whichthe generator is driven for canceling a vibration of the engine.
 17. Thedrive control apparatus in accordance with claim 16, further comprising:an engine speed measuring device for measuring an engine speed of theengine; and an intake-pipe negative-pressure measuring device formeasuring an intake-pipe negative pressure, wherein: the control partdetermines whether the generator is driven for canceling the vibrationof the engine based on results of measurements by the engine speedmeasuring device and the intake-pipe negative-pressure measuring device.18. The drive control apparatus in accordance with claim 12, furthercomprising: a required driving force measuring device for measuring arequired driving force of the vehicle; and a vehicle speed measuringdevice for measuring a vehicle speed of the vehicle, wherein: when thevehicle speed measured by the required driving force measuring device islower than or equal to a predetermined value, and the required drivingforce measured by the required driving force measuring device is largerthan or equal to a predetermined value, the control part performs an EVmode in which the clutch is disconnected and the driving force of thevehicle is generated by the motor.